New optical and electric-field assisted fluidic pick and place technique

Electrophoresis is a classical electrochemical transport process, which is based on the migration of charged particles in a suspension by the influence of an electric field. One of the important applications of this technique is the study of DNA/RNA hybridization on bio-electronic chips. However, electrophoretic pick and place techniques are currently limited to the serial `pick' and `place' of individual devices or materials. There is a need for the rapid and parallel pick-and-place of individual devices to particular locations on a host substrate. In this paper, we present a novel electrochemical system for non-lithographic, field assisted, fluidic pick and place assembly of devices on a silicon substrate by means of electrical and optical addressing. The methodology presented here can be applied to massively parallel assembly of large semiconductor arrays (>1000×1000) with fast (approximately a few seconds) and accurate positioning for a wide range of device sizes (0.8-100 μm). In our experiments, an electrochemical cell was used with Indium Tin Oxide (ITO) and an n-type Silicon substrate as the two electrode materials and de-ionized water (R = 18 MΩ) as the electrolytic medium between the two electrodes. Negatively charged polystyrene beads (0.8 μm, 10 μm, and 20 μm in diameter), 50-100 μm diameter negatively charged (by immersing SDS detergent) SiO₂ pucks and 100 μm diameter light emitting diodes were successfully positioned on Silicon substrates by electrical addressing. In addition, 0.8 μm diameter beads were patterned on a un-patterned Silicon substrate by optical addressing.